Enhanced ferromagnetism in half-metallic CoIrZrAl quaternary Heusler alloy: A density functional study

The possibility of synthesis of the quaternary Heusler alloy CoIrZrAl is proposed on the basis of first-principles Density Functional calculations. The equilibrium lattice constant, assuming F-43 m lattice symmetry, is calculated and the Bulk modulus obtained is very close to that of $C{o}_2$ZrAl (Essaoud and Jbara, 2021). CoIrZrAl Heusler alloy is predicted to be a half-metal having an energy gap of 0.7632 eV between $t_{1u}$ and $e_u$ state in the spin down channel. The ferromagnetic state is the magnetic ground state where the main source of total magnetic moment (= 1${\mu }_B$) is the unpaired electron in the $e_u$ state derived from Co-3d and Ir-5d electrons. Upon 50% doping at the Co-site (3d) by an Ir atom having extended 5d state increases the mean field estimate of $T_C$ over ${\mathrm{Co}}_2$ZrAl. The charge density difference profile clearly establishes that the exchange mechanism is super-exchange between hybrid Co-3d electrons and Ir-5d electrons mediated by their hybridization with Zr-4d electrons. The partial replacement of the Co-3d electrons with less localized Ir-5d electrons leads to robust ferromagnetism and robust half-metallicity under hydrostatic pressure.